It is known that the lateral control of an aircraft, in particular of a civil or military transport aircraft, implemented by a usual autopilot device, can be carried out in general in three different ways, namely:                by fixing a heading instruction;        by fixing a track instruction; or        by slaving the path of the aircraft to a path which is defined with respect to the ground (and which follows either a succession of beacons situated on the ground or GPS coordinates to be flown over), this path being called the flight plan.        
These different piloting modes can be matched with a maximum roll limit which can be chosen by the pilot or which can be contained in the autopilot device. When there is a change of path, the roll rate is therefore kept within this maximum roll limit.
It is known that, during operations carried out by a civil or military aircraft, the aircraft can be brought to join (or acquire) a flight path horizontally and to do this whilst complying, during this acquisition phase, with a roll instruction which is imposed by the pilot. This flight path can notably be an in-flight refuelling path, an approach path or any other path which is defined geographically with respect to the ground. During such a flight phase, the impact of variables (aircraft speed, altitude, wind, etc.) and their variation with respect to time have a significant effect of the future path of the aircraft. Taking these variables into account is therefore essential for the correct completion of the flight path acquisition manoeuvre.
In the case of piloting by heading (or by track), only the heading (or the track) is considered as important. The autopilot device must therefore reach this heading (or track) instruction whilst complying with the structural and/or comfort limits of the passengers of the piloted aircraft. The position of the aircraft, when it has achieved this instruction, is not therefore known in advance because it depends on parameters which are variable such as the roll rate, the wind, etc.
Moreover, in the case of piloting according to a flight plan, the final position of the aircraft is known if and only if beacons situated on the ground can be selected in the zone in question. However, in order to carry out such piloting, it is necessary to modify the flight plan, such a modification representing a large amount of manipulation which is not very reactive (several seconds generally elapse before the instruction is taken into account).
Consequently, none of these usual solutions is completely satisfactory for automatically acquiring a flight path (in-flight refuelling path, approach path, etc.) in compliance with a roll instruction.